The invention relates to a heat shield for shielding an object against heat and/or noise, which has at least one metal layer, with embossments projecting beyond at least one of the surfaces thereof.
Heat shields of this type are used as noise and/or heat protectors for other components. Heat shields are used, for example, in engine compartments of motor vehicles, in particular in the area of the exhaust system, to protect adjacent temperature-sensitive components and assemblies from excessive heating. The heat shields are often used simultaneously as a noise absorber.
To be able to absorb noise and shield heat to a sufficient extent, heat shields of this type frequently have an at least three-layered structure. The two cover layers typically comprise metal, in particular steel, aluminum-plated steel, or aluminum (alloy). A nonmetallic insulation layer is embedded between the cover layers. It comprises, for example, mica or vermiculite, temperature-resistant cardboard, inorganic or organic fiber composite materials, or other suitable insulation materials such as fabrics, knitted fabrics, and/or warp made of temperature-resistant fibers. The nonmetallic inlays cause increased effort in regard to the recycling of the heat shields and are therefore often undesirable.
Heat shields are also known which entirely comprise metal and do not have a nonmetallic insulation layer. The metal layers are often shaped in such a way that a resonance chamber is formed between them, in which noise may be absorbed. The air layer enclosed between the metal layers is simultaneously used as the insulation layer against heat. The resonance chambers are formed, for example, in that embossments or ribs are shaped into one or both metal layers, which project in the direction toward the respective other metal layer. In addition, shaping ribs or embossments into the metal layers of heat shields for stiffening is known.
As a function of the particular application, especially the space available, heat shields often have a strong three-dimensional conformation which may result in tensions in the heat shield. Because of the vibrations during operation, the heat shields may be damaged in the high-tension sections in particular and form cracks which often crack further upon continuing operation, because the heat shields are to be designed as thin as possible—also in regard to saving material and weight. Upon the three-dimensional deformation of the heat shields, strong, often non-reproducible wrinkling additionally occurs, which negatively influences the reflection properties of the heat shield surface. Moreover, cracks may already occur in very strongly deformed areas during the manufacturing upon the three-dimensional deformation of the heat shield from a planar basic shape, which make the heat shield unusable from the beginning.
Stiffening ribs or embossments may—as noted—help to achieve the required rigidity of the metal layers. In the case of embossments, distributing them uniformly and of equal size over the metal layer is known. The protective effect and stability of the heat shield is thus improved, but the problems cited in the preceding paragraph are not always reliably remedied in this way. An especially high degree of deformation actually occurs particularly in the area of the embossments, which results in an increased danger of cracking or, vice versa, requires the use of higher material thicknesses, which has negative effects in regard to cost and weight, however. To avoid cracking in any case, the embossments may also be implemented relatively small. However, the desired stiffening of the metal layer may then often not be achieved, and the noise absorption properties are also not optimal.
There is therefore a need for a heat shield which, with the lowest possible material consumption and weight, is nonetheless as stable as possible, does not tend toward cracking, and offers good noise and heat protection. Furthermore, uncontrolled wrinkling is to be avoided. The object of the invention is accordingly to specify a heat shield which does not have the above disadvantages.